Transpiration stomatal

Growth and physiological processes (leaf photosynthesis, transpiration, stomatal conductance. 

Collatz, G. Ball, J. T., Grivet, C. and Berry, J. A. (1991). Physiological and environmental regulation of stomatal conductance, photosynthesis, and transpiration a model that includes a laminar boundary layer, Agric. For. Meteorol. 54,107-136. 

Jarvis, P.G. McNaughton, K.G. (1985). Stomatal control of transpiration Scaling up from leaf to region. Advances in Ecological Research, 15, 1-49. 

Adaptive features of stomata - rapid closure in response to turgor loss (and perhaps other stimuli) - which reduce transpiration when plants become stressed. Alternatively, for ephemer-als, maintenance of high stomatal conductance and photosynthetic capacity to permit maximum growth rate during the limited time that water is available. 

Atrazine enters plants primarily by way of the roots and secondarily by way of the foliage, passively translocated in the xylem with the transpiration stream, and accumulates in the apical meristems and leaves (Hull 1967 Forney 1980 Reed 1982 Wolf and Jackson 1982). The main phytotoxic effect is the inhibition of photosynthesis by blocking the electron transport during Hill reaction of photosystem II. This blockage leads to inhibitory effects on the synthesis of carbohydrate, a reduction in the carbon pool, and a buildup of carbon dioxide within the leaf, which subsequently causes closure of the stomates, thus inhibiting transpiration (Stevenson et al. 1982 Jachetta et al. 1986 Shabana 1987). 

The effect of zearalenone on crop development may be connected to its influence on the status and functioning of the photosynthetic apparatus (Koscielniak et al. 2008). The after-effects of zearalenone on the growth of soybean and wheat plants, net photosynthesis and transpiration rates, stomatal conductance, photochemical efficiency of photosystem 2 and on final seeds yield were determined. Modifications in leaf area were more pronounced in soybean than in wheat, and this tendency increases in successive developmental phases. The net photosynthesis was stimulated during the juvenile phase and during that of the final one by about 13.6% (average) in soybean plants. Stimulation of transpiration was also observed after... 

Plant water status is affected by environmental pollution and consequently influences plant function at every level of biological organisation. It can be characterized by measurements of the relative water content (RWC), the water deficit, the water potential ( P ) and the osmotic potential ( Fq), along with transpiration rate and stomatal resistance. Since for the latter four parameters, tissue samples are removed from the plant, they are usually determined in the end of an experiment. If several sampling times are needed, then additional plants/replicates must be included. 

Transpiration rate and stomatal resistance are the most commonly measured plant gas exchange parameters using IRGA. Their behaviour in A. thaliana plants exposed to heavy metal ion stress is demonstrated in Figure 2 B and C. 

Todd and Todd and Probst also measured the effects of ozone (at 4 ppm for 40 min) on photosynthesis and found that development of symptoms was associated with inhibition of carbon dioxide fixation. This effect was also confirmed by Macdowall, who reported that the inhibition of photosynthesis was greater than that which could be accounted for by chlorophyll destruction. Hill and Littlefield associated decreased net photosynthesis caused by ozone (at 0.06 ppm for 1 h) with both stomatal opening and rates of transpiration. These studies have generally shown that net photosynthesis can decrease without visible injury. 

Two reports based on rather gross measuring techniques found a close correlation between ozone uptake and transpiration. These studies indicated that stomatal control is the prime factor in controlling pollutant uptake and that cuticular sorption is negligible in relation to stomatal absorption. These findings are generally supported by past work that indicates that stomata are the prime sites of pollutant entry... 

Hill, A. C., and N. Littlefield. Ozone. Effect on apparent photo thesis, rate of transpiration, and stomatal closure In plants. Environ. Sci. Technol. 3 52-56, 1969. 

Figure 17.11 Neil Yorio at NASA s Kennedy Space Center taking leaf porometer measurements with potatoes to monitor stomatal conductance and transpiration rates. When measurements were taken at 400 ppm CO2, a mask was worn to removed exhaled breath from the chamber to avoid elevating the CO2 concentration.

Figure 17.12 Stomatal conductance of potatoes grown at 400, 1000, and 10 000 ppm carbon dioxide. Conductance and transpiration were lowest at 1000 ppm and highest at 10 000 ppm. Super-elevated concentrations like 10 000 ppm might can occur in closed environments in space (source Wheeler et al., 1999).

The physiology of stomatal movement has been extensively researched. Early studies using phenylmercuric acetate demonstrated that the induced closure of stomata could conserve water significantly up to one month from the time of treatment. Although reductions in transpiration would probably carry a yield penalty, the long-term benefits of increased land use are desirable. However, no commercially viable anti-transpirants have been produced. 

The primary inhibitory effect of cadmium on photosynthesis of excised leaves was proposed to be metal-induced stomatal closure (Bazzaz et al., 1974 Lamoreaux and Chaney, 1978). In epidermal peels floating on a metal-containing solution, stomatal closure was reported (Bazzaz et al., 1974). Inhibition of transpiration by several metals, especially by cadmium, is well documented (Poschenrieder et al., 1989), but is not necessarily at the stomatal level. Metal-induced stomatal closure can indirectly be responsible for a decrease of photosynthetic C02 fixation indeed. However, several enzymes of the Calvin cycle are directly affected by metals. 

Evidence was obtained recently that pesticide vapors may enter the air by still another mechanism, involving plant circulation and water loss (57). Rice plants were found to efficiently transport root-zone applied systemic carbamate insecticides via xylem flow to the leaves, eventually to the leaf surface by the processes of guttation and/or stomatal transpiration, and finally to the air by surface volatilization. Results from a model chamber showed that 4.2, 5.8, and 5.7% of the residues of carbaryl, carbofuran, and aldicarb, respectively, present in rice plants after root soaking vaporized within 10 days after treatment. The major process was evaporation of surface residues deposited by guttation fluid. 

One characteristic activity of ABA is its effect on stomata, which protects plants from water stress. At 10 7moll 1, ABA given through a transpiration stream from cut ends of shoots causes stomatal closure.702 The activity is more effective in epidermal strips floated on a buffer solution than in shoots. At 10-10 mol 1 1, ABA closes stomata in epidermal strips at pH 5.5.703 The activity at pH 6.8 is 103 times lower than that at pH 5.5, suggesting that the active form of ABA is not a dissociated acid but an undissociated acid. The simulation study... 

The pathway of least resistance for gases to cross an epidermis—and thus to enter or to exit from a leaf—is through the adjustable space between a pair of guard cells (Fig. 1-2). This pore, and its two surrounding guard cells, is called a stoma or stomate (plural stomata and stomates, respectively). When they are open, the stomatal pores allow for the entry of CO2 into the leaf and for the exit of photosynthetically produced O2. The inevitable loss of water vapor by transpiration also occurs mainly through the stomatal pores, as we will discuss in Chapter 8 (Section 8.1B). Stomata thus serve... 

For our applications to transpiration and photosynthesis, we will define a stomatal conductance, and a stomatal resistance, r for the diffusion of species j using Equation 8.4 ... 

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